A mercapto compound has heretofore been widely used as synthetic raw materials for various medicines and agrochemicals. Above all, a β-mercapto carbonyl compound is recognized for the usefulness as an antioxidant, and is industrially utilized as a stabilizer for a polymeric compound (see Japanese Patent Laid-Open Publication No. 2003-252918; Patent Document 1).
As one of methods for producing a β-mercapto carbonyl compound, there is a known method in which an α,β-unsaturated carboxylic acid and hydrogen sulfide are subjected to a Michael addition reaction.
Also, it is reported that a Michael addition reaction using acrylic acid as the α,β-unsaturated carboxylic acid proceeds by using hydrogen sulfide in the presence of diethylamine (see Acta Chimica Scandinavica 1951, 5, 690-698; Non-Patent Document 1).
However, in the method using the reaction described in Non-Patent Document 1, the productivity is low because diethylamine is used in large excess and the reaction takes a long time. Therefore, in order to produce a β-mercapto carbonyl compound industrially and efficiently, there remains a problem that recovery equipment for diethylamine is necessary.
Further, it is reported that β-mercaptopropionic acid can be synthesized by reacting acrylic acid with sodium hydrosulfide in the presence of a large excess of sodium hydroxide (see Japanese Patent Laid-Open Publication No. 2001-187778; Patent Document 2).
In this method, however, 5 or more equivalents of sodium hydroxide relative to the substrate are needed in order to suppress a side reaction, and the excess alkali is needed to be neutralized with an acid. Therefore, a large amount of the inorganic salt generated is required to be disposed of, and there has been a problem that this method is not suitable for the industrial production.
Further, Japanese Patent Laid-Open Publication No. 2001-354643 (Patent Document 3) and Japanese Patent Laid-Open Publication No. 2001-354644 (Patent Document 4) disclose a method for producing sulfurized olefins in which olefins are sulfurized by using sulfur derivatives and hydrogen sulfide in the presence of a solid acid catalyst such as zeolite and the like.
In Patent Documents 3 and 4, there are descriptions about the generation of mercaptan as an intermediate. However, in these documents, the final target compound is not the mercapto compound which is the objective compound of the present invention, but organic sulfides, disulfides, and polysulfide. Therefore, the generation of the mercaptan corresponding to the mercapto compound is suppressed as low a level as possible.
Further, Patent Documents 3 and 4 describe that the raw material olefins may be diluted with a solvent but the solvents described therein are saturated aliphatic hydrocarbons such as methane, ethane, pentane, and the like, namely non-polar solvents. There is no description, and no suggestion about using a polar solvent which is compatible with a polar solvent such as water and the like. Further, there is no description about the effect thereof.    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-252918    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-187778    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-354643    [Patent Document 4] Japanese Patent Laid-Open Publication No. 2001-354644    [Non-Patent Document 1] Acta Chimica Scandinavica 1951, 5, 690-698